A control channel may be used to transmit control information regarding a mobile device from a network component, such as a base station or a base node. Control information may include information regarding resource assignments, modulation and coding scheme, power control, precoding and/or other information for controlling the operation of a mobile device or a group of mobile devices. In Long Term Evolution (LTE) and LTE-Advance (LTE-A) standards, a Physical Downlink Control Channel (PDCCH) contains a message transmitted by a network component known as a Downlink Control Information (DCI) message. For simplicity, a control information message will be referred to herein as simply a CI, and a DCI message will simply be referred to herein as a DCI. Several DCIs can generally be transmitted in a subframe. In a multiple user system, DCIs may be transmitted that are intended for all users within a cell. Other DCIs may be intended only for a specific mobile station. Different DCI formats may be used for carrying different types of control information. Information regarding specific DCI formats, in LTE systems, can be found in TS 36.212, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding (Release 8)” Section 5.3.3, Version 8.8.0, 2009-12, the entire contents of which are incorporated by reference.
Multiple control channel formats are possible. Conventionally, a mobile device will not know the format of a control channel carrying a CI for the mobile station before a subframe containing the CI is received. A “blind” decoder in the mobile device may decode several hypothetical or “candidate” control channel formats in an attempt to decode CI intended for the mobile device. A CI that might have been transmitted on a candidate control channel may be referred to herein as a “possible CI”. A mobile device may identify whether it has received a CI transmission correctly by means of a Cyclic Redundancy Check (CRC) appended to each CI for error detection. The CRC may, for example in LTE and LTE-A, be 16-bits in length. Typically, each CRC is scrambled with the intended mobile device identity, known as Radio Network Temporary Identifier (RNTI), to reduce PDCCH transmission payload (see TS 36.211, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 8)”, Version 8.9.0, 2009-12, Section 5.3.3.2). The RNTI identifies the mobile station for which a CI is intended. Scrambling the CRC with the RNTI, while increasing efficiency by reducing the total number of bits that must be transmitted, also increases the probability of CI false detection for the PDCCH blind decoder unit in the mobile device.
In an LTE system, a mobile device may monitor a set of possible or “candidate” PDCCHs. Multiple aggregation levels (e.g. 1, 2, 4, 8) are defined by “search spaces”, each search space having set of candidate PDCCHs. Each candidate PDCCH may include a defined group of Control Channel Elements (CCEs) that each, in turn, includes a defined group of Resource Elements (REs). Both common search spaces and mobile device-specific search spaces are defined in an LTE system. In an LTE system, for each subframe, there are a maximum of 22 candidate PDCCHs that a blind decoder may attempt to decode. For each of the candidate PDCCHs, two different DCI payload sizes are possible, and thus a blind decoder may make a maximum of 44 attempts for each subframe to decode a DCI.
Since each possible type of CI has defined structure, conventional CI false detection reduction may be done in the CI parsing unit in software after a blind decoder. However, possible false detected CIs can pass the parsing unit, and throughput performance may be harmed by falsely detected CIs.